Browsing by Author "Brizzolara, Stefano"

Now showing 1 - 20 of 66
  • Thumbnail Image
    Adjustable Energy Saving Device for Transom Stern Hulls
    Salian, Rachit Pravin (Virginia Tech, 2019-05-10)
    The study presents a numerical investigation about the hydrodynamic characteristics of a transom mounted interceptor on the Oliver Hazard Perry class frigate (FFG-7), in order to assess the potential of propulsion power reduction in a wide range of speeds. This study is aimed to design a stern interceptor with optimal efficiency not only at top speed, but also cruising/transfer speeds, by a simple regulation of its variable geometrical characteristics (from a construction and operational standpoint). A high fidelity numerical model is developed in the open source CFD suite OpenFOAM for the prediction of the longitudinal dynamic equilibrium at speed and the total resistance characteristics of the bare hull. The Reynolds Averaged Navier-Stokes Equations are solved using interDyMFoam, a multiphase volume of fluid solver which allows for a dynamic mesh. The numerical model is validated using the results of the experimental model tests conducted on a 1/80th scale model at the United States Naval Academy Hydromechanics Laboratory (NAHL). The validated numerical model is used to predict the hydrodynamic characteristics of the transom mounted interceptor at different interceptor settings and speeds. The results show that the interceptor reduces the amount of resistance, the running trim, and the sinkage of the ship at high speeds. For a speed of 0.392 Froude number (Fr), a drag reduction of 3.76% was observed, as well as a significant reduction in trim.
  • Thumbnail Image
    Aerodynamic and Aeroacoustic Analysis of Low Reynolds Number Propellers Using Higher-Order RANS Transition Turbulence Modeling
    Pisharoti, Naina (Virginia Tech, 2024-06-05)
    The advent of advanced vehicle concepts involving Urban Air Mobility (UAM) and small Unmanned Aerial Systems (sUAS) has brought about a new class of rotorcraft technology which operate predominantly in low-Reynolds ($Re$) number regimes. In such regimes, the flow experiences complex boundary layer phenomena like laminar separation, flow transition and reattachment. These effects are known to greatly alter the flow at and near the rotor wall, influencing its aerodynamic performance as well as the noise generated. Capturing these effects in our computational models is necessary to further our understanding of rotor aerodynamics and acoustics. The current study has introduced a novel RANS transition turbulence model, SSG/LRR-$\omega$-$\gamma$, that is capable of modeling different modes of transition involving natural, bypass, separation-induced and crossflow transition. The model framework uses a Reynolds stress transport model, SSG/LRR-$\omega$, as the base turbulence formulation and is coupled with Menter's $\gamma$ transition model. It was validated using a number of canonical cases that exhibited different transition mechanisms and the model performed equivalently or better than existing state-of-the-art transition models. It is worthy to note that the proposed model was able to perform well in three-dimensional flows, demonstrated using the case of a prolate spheroid. This underscores the capability of Reynolds stress models to accurately capture complex flow curvatures, improving upon the capabilities of linear eddy viscosity models. The transition model, integrated into OpenFOAM, was then employed to analyze two different UAV propellers. The rotor flow was examined using a URANS simulation with an overset grid. The objective was twofold: firstly, to validate the predictions generated by the proposed model for low-Reynolds number (low-$Re$) rotors, and secondly, to evaluate its effectiveness across a range of operating conditions. Comparisons were drawn against established fully turbulent and transition models. The analysis showed that transition models in general tended to be consistent in their predictions and less sensitive to changing operating conditions when compared to fully turbulent models. They also demonstrated the ability to accurately predict the mechanisms leading to separation and transition. Further, the proposed transition model demonstrated superior capability in capturing detailed flow features, particularly in the wake, compared to other fully turbulent and transition models, which is attributed to its Galilean invariant framework. To leverage the boundary layer information obtained from the proposed model, a semi-empirical broadband noise prediction method was implemented. This method utilized boundary layer data predicted by URANS simulations to estimate blade self-noise. An evaluation of the fully turbulent $k$-$\omega$ SST model and the proposed transition model revealed that both exhibited reasonable accuracy at lower rotor advance ratios. However, the transition model performed better at higher advance ratios. It was also observed that CFD-based approaches provided superior prediction accuracy compared to lower-fidelity aerodynamic models in the context of blade self-noise prediction Finally, the proposed aerodynamic and acoustic computational framework was applied to a design case study of swept propellers to understand the advantages of blade sweep on rotor aerodynamics and noise. A qualitative analysis of the flow suggested that the swept rotor exhibited lower levels of blade wake interaction compared to the unswept geometry, in line with the experimental observations.
  • Thumbnail Image
    Anisotropic Turbulence Models for Wakes in an Active Ocean Environment
    Wall, Dylan Joseph (Virginia Tech, 2021-07-13)
    A set of second-moment closure turbulence models are implemented for the study of wake evolution in an oceanic environment. The effects of density stratification are considered, and the models are validated against laboratory experiments mimicking the stratified ocean environment, and against previous experimental study of wakes subjected to a density stratification. The turbulence models are found to reproduce a number of important behaviors which differentiate stratified wakes from those in a homogeneous environment, including the appropriate decay rates in turbulence quantities, buoyant suppression of turbulence length scales, and canonical stages in wake evolution. The existence of background turbulence is considered both through the introduction of production terms to the turbulence model equations and the replication of scale-resolved simulations of wakes embedded in turbulence. It is found that the freestream turbulence causes accelerated wake growth and faster decay of wake momentum. Wakes are then simulated at a variety of Re and Fr representative of full-scale vehicles operating in an ocean environment, to downstream distances several orders of magnitude greater than existing RANS studies. The models are used to make some general predictions concerning the dependence of late-wake behavior on these parameters, and specific insights into expected behavior are gained. The wake turbulence is classified using "fossil turbulence" and stratification strength criteria from the literature. In keeping with experimentally observed behavior, the stratification is predicted to increase wake persistence. It is also predicted that, regardless of initial Re or F r, the wake turbulence quickly becomes a mixture of overturning eddies and internal waves. It is found that the high Re wakes eventually become strongly affected by the stratification, and enter the strongly-stratified or LAST regime. Additional model improvements are proposed based on the predicted late wake behavior.
  • Thumbnail Image
    An Approach for Computing Parameters for a Lagrangian Nonlinear Maneuvering and Seakeeping Model of Submerged Vessel Motion
    Jung, Seyong; Brizzolara, Stefano; Woolsey, Craig A. (IEEE, 2021-07-01)
    In this study, hydrodynamic forces on a submerged vessel maneuvering near a free surface are determined using a reformulated Lagrangian nonlinear maneuvering and seakeeping model derived using Lagrangian mechanics under ideal flow assumptions. A Lagrangian mechanics maneuvering model is first reformulated to simplify the computation of parameters; then, incident wave effects are incorporated into the reformulation; finally, the parameters are computed using a medium-fidelity time-domain potential-flow panel code. Predictions from the reformulated Lagrangian nonlinear maneuvering and seakeeping model, whose parameters are computed using the methods described here, are compared with direct numerical computations in two steps for a prolate spheroid maneuvering in the longitudinal plane near the free surface. First, the hydrodynamic force and moment predicted by the model are compared with solutions from the panel code for sinusoidal motion in surge, heave, and pitch in calm water. Second, the hydrodynamic force and moment are investigated for cases where the spheroid maneuvers to approach the surface in calm water and in plane progressive waves. To conclude, a physically intuitive formulation of the Lagrangian nonlinear maneuvering and seakeeping model is presented for control applications and simulations.
  • Thumbnail Image
    An Approach for Computing Parameters for a Lagrangian Nonlinear Maneuvering and Seakeeping Model of Submerged Vessel Motion
    Jung, Seyong; Brizzolara, Stefano; Woolsey, Craig A. (IEEE, 2021-03)
    In this study, hydrodynamic forces on a submerged vessel maneuvering near a free surface are determined using a reformulated Lagrangian nonlinear maneuvering and seakeeping model derived using Lagrangian mechanics under ideal flow assumptions. A Lagrangian mechanics maneuvering model is first reformulated to simplify the computation of parameters; then, incident wave effects are incorporated into the reformulation; finally, the parameters are computed using a medium-fidelity time-domain potential-flow panel code. Predictions from the reformulated Lagrangian nonlinear maneuvering and seakeeping model, whose parameters are computed using the methods described here, are compared with direct numerical computations in two steps for a prolate spheroid maneuvering in the longitudinal plane near the free surface. First, the hydrodynamic force and moment predicted by the model are compared with solutions from the panel code for sinusoidal motion in surge, heave, and pitch in calm water. Second, the hydrodynamic force and moment are investigated for cases where the spheroid maneuvers to approach the surface in calm water and in plane progressive waves. To conclude, a physically intuitive formulation of the Lagrangian nonlinear maneuvering and seakeeping model is presented for control applications and simulations.
  • Thumbnail Image
    Architecture Flow Optimization - Refinement and Application for Naval Ship Concept Design
    Bonsall, Jaxson Todd (Virginia Tech, 2024-05-31)
    This thesis describes the refinement of an Architecture Flow Optimization (AFO) tool for naval surface ship design, specifically focusing on the development of new network and matrix-based methods for AFO formulation and their application in Concept Development. The AFO tool analyzes and optimizes the flow of energy through the ship's Vital Components (VCs) interfacing with a Ship Synthesis and Product Model (SSM), ensuring that all physical and operational constraints are satisfied while minimizing system cost across multiple intact and damaged operational scenarios. The total ship system is described by physical and logical architectures in a network structure comprised of vital component nodes and arcs. These elements form the basis of a linear system of equations in matrix form, the manipulation of which relies heavily on linear algebra and matrix operations. The matrix system of equations is solved using linear programming with a significant improvement in computational efficiency. The solution supports the sizing of individual vital components and the refinement of system logical architecture. It also provides the basic AFO engine necessary to support future refinement of a dynamic architecture flow optimization (DAFO) with the computational speed necessary for rapid solution of dynamic mission scenarios insuring optimized and feasible warfighting reconfiguration, with and without damage.
  • Thumbnail Image
    An Assessment of the CFD Effectiveness for Simulating Wing Propeller Aerodynamics
    Shah, Harshil Dipen (Virginia Tech, 2020-06-02)
    Today, we see a renewed interest in aircraft with multiple propellers. To support conceptual design of these vehicles, one of the major needs is a fast and accurate method for estimating wing aerodynamic characteristics in the presence of multiple propellers. For the method to be effective, it must be easy to use, have rapid turnaround time and should be able to capture major wing–propeller interaction effects with sufficient accuracy. This research is primarily motivated by the need to assess the effectiveness of computational fluid dynamics (CFD) for simulating aerodynamic characteristics of wings with multiple propellers. The scope of the present research is limited to investigating the interaction between a single tractor propeller and a wing. This research aims to compare computational results from a Reynolds-Averaged Navier-Stokes (RANS) method, StarCCM+, and a vortex lattice method (VLM), VSP Aero. Two configurations that are analysed are 1) WIPP Configuration (Workshop for Integrated Propeller Prediction) 2) APROPOS Configuration. For WIPP, computational results are compared with measured lift and drag data for several angles of attack and Mach numbers. StarCCM+ results of wake flow field are compared with WIPP's wake survey data. For APROPOS, computed data for lift-to-drag ratio of the wing are compared with test data for multiple vertical and spanwise locations of the propeller. The results of the simulations are used to assess the effectiveness of the two CFD methods used in this research.
  • Thumbnail Image
    Bearing Estimation for Underwater Acoustic Source Using Autonomous Underwater Vehicle
    Murali, Rohit (Virginia Tech, 2022-07-07)
    This thesis describes the challenges involved in detecting sources of acoustic noise using an autonomous underwater vehicle (AUV) in real world environments. The initial part of this thesis describes the developments made for redesigning an acoustic sensing system that can be used to estimate the relative bearing between a source of acoustic noise and an AUV. With an estimate of the relative bearing, the AUV can maneuver toward the source of noise. The class of algorithms that are used to estimate bearing angle are known as beamforming algorithms. A comparison of the performance of a variety of beamforming algorithms is presented. When estimating the bearing to a source of noise from a small AUV, the noise of the AUV, especially its propulsor, pose significant challenges. Toward the goal of active cancellation of AUV self-noise, we propose placing an additional hydrophone inside the AUV in order to estimate the AUV self-noise that appears on the exterior hydrophones that are used for bearing estimation.
  • Thumbnail Image
    CFD-informed Lumped Parameter Models Result In High-Fidelity Maneuvering Predictions of AUVs
    Miller, Lakshmi Madhavan (Virginia Tech, 2023-07-11)
    Recent developments in autonomous underwater vehicles (AUV) have created the need for a low cost AUV that is comparable in class and payload capabilities to existing, commercially available, expensive and sub-optimal crafts. The Navy is active in research of autonomous, unmanned, highly efficient, high speed underwater craft. Small, low cost AUVs capable of swarm control are of special interest for military mine applications. No matter the nature of the application or class of craft, a common challenge is the accuracy of maneuvering predic- tions. Maneuvering predictions not only affect design, but also the real time understanding of mission capabilities and endurance. Thus the proliferation of AUVs in recent times for commercial and defense applications have led to the need of higher fidelity of physics based lumped parameter models. The sensor data, along with maneuvering model data can tie into a more accurate trajectory. Multiple such incremental advances in the literature for prediction of maneuvering shall lead to a more accuracy. This work hopes to bridge some important gaps that ensure the creation of such a non-linear LPM to predict the maneuver- ing characteristics of an AUV using non linear hydrodynamic derivatives obtained through static and dynamic CFD. This model shall be implemented for the craft designed for DIVE technologies, our industrial sponsor and an in-house craft, the 690. This model shall also be made generalized for most submerged craft with a torpedo or slender hull form, with cruciform or X configuration of fins. This dissertation looks to provide the framework to identify CFD informed high fidelity dynamic model for AUVs. The model thus created shall be spe- cialized to account for specific important effects such as flow interaction among appendages, effect of using steady and unsteady maneuvers as CFD information and kinematic charac- teristics of captive maneuvers. The specific, innovative contributions in this dissertation are listed below: 1. Definition of a new stability index to incorporate effects of gravity at low-moderate speeds 2. Novel method for identification of hydrodynamic derivatives 3. Systematic and comprehensive study on the parameters affecting VPMM
  • Thumbnail Image
    Characterization of Liquid Metal Free Surface Response to an Electromagnetic Impulse and Implications for Future Nuclear Fusion Devices
    Weber, Daniel Perry (Virginia Tech, 2024-01-10)
    Liquid metals (LMs) are compelling candidates for use as plasma facing components (PFCs) in fusion devices to mitigate heat loading, limit damage due to erosion, and possibly breed tritium. When used as electrodes, such as in z-pinch devices, PFCs are subject to large current and magnetic flux densities resulting in large Lorentz forces. Furthermore, if the PFCs are LM, the forces excite wave behavior that has not previously been investigated. The work presented here first characterizes the response of LMs to current pulses which peak between 50 and 200 kA and generate magnetic pressures between 0.5 and 5 MPa. High-speed videography records the liquid metal free surface during and after the current pulse and captures a fast moving, annular jet of LM emerging from the main body. The vertical velocities of the jet range from 0.6 to 5.3 m/s which is consistent with hydrodynamic predictions. Ejection of small droplets is observed from the LM immediately after the current pulse, preceding the LM jet, with velocities ranging from −3.1 to 18.9 m/s in the vertical direction and −14.3 to 6.3 m/s in the radial. A statistical model is developed to predict the likelihood of certain LM PFC material contaminating a core plasma and the severity in such an event. Lastly, effectiveness of bulk wave movement mitigation is investigated with two solid barrier designs, a cylindrical and conical baffle. These designs were fabricated after an iterative design process with assistance from hydrodynamic simulations. A cylindrical baffle design is shown to be preferable for integration into future fusion devices for the reduced likelihood of interference with plasma column formation.
  • Thumbnail Image
    Data-Driven, Non-Parametric Model Reference Adaptive Control Methods for Autonomous Underwater Vehicles
    Oesterheld, Derek I. (Virginia Tech, 2023-11-03)
    This thesis details the implementation of two adaptive controllers on autonomous underwater vehicle(AUV) attitude dynamics starting from the standard six degree-of-freedom dynamic model. I apply two model reference adaptive control (MRAC) algorithms which make use of kernel functions for learning functional uncertainty present in the system dynamics. The first method extends recent results on model reference adaptive control using reproducing kernel Hilbert space (RKHS) learning techniques for some general cases of multi-input systems. The first controller design is a model reference adaptive controller (MRAC) based on a vector- valued RKHS that is induced by operator-valued kernels. This paper formulates a model reference adaptive control strategy based on a dead zone robust modification, and derives conditions for the ultimate boundedness of the tracking error in this case. The second controller is an implementation of the Gaussian Process MRAC developed by Chowdhary, et al. I discuss the method of each of these algorithms before contrasting the underlying theoretical structure of each algorithm. Finally, I provide a comparison of each algorithm's performance on the six degree-of-freedom dynamic model of the Virginia Tech 690 AUV and provide field trial results for the RKHS based MRAC implementation.
  • Thumbnail Image
    Deactivation Diagram Development for Naval Ship System Vulnerability Analysis
    Snyder, Daniel Joseph (Virginia Tech, 2019-06-17)
    System architecture analyses of distributed ship systems offer a practical view of system behavior over all operational states; however, the effectiveness of these analyses can be bound by limited computational performance or capability. Deactivation diagrams provide an alternative view to conventional system architecture descriptions, allowing for rapid analysis of system connectivity and flow based on precomputed single-state system descriptions. This thesis explores the development of system deactivation diagrams and their use in early-stage naval ship system design. Software tools developed in C++ and VBA as part of this research support the Virginia Tech (VT) Naval Ship Design Concept and Requirements Exploration (CandRE) process and tools utilizing the U.S. Navy's Leading-Edge Architecture for Prototyping Systems (LEAPS) framework database. These tools incorporate automated path-finding algorithms developed based on proven network theory and effective computational methods for use in performing ship system deactivation analysis. Data drawn from the results of this approach possess extensible applicability towards studies in naval ship system vulnerability, flow optimization, network architecture, and other system analyses. Supplementary work on interfacing the LEAPS framework libraries with deactivation analyses has demonstrated the capability for generating deactivation diagrams from complex LEAPS ship system databases and paved the way for future incorporation of LEAPS into research work at Virginia Tech.
  • Thumbnail Image
    Deceleration Stage Rayleigh-Taylor Instability Growth in Inertial Confinement Fusion Relevant Configurations
    Samulski, Camille Clement (Virginia Tech, 2021-06-08)
    Experimental results and simulations of imploding fusion concepts have identified the Rayleigh-Taylor (RT) instability as one of the largest inhibitors to achieving fusion. Understanding the origin and development of the RT instability will allow for the development of mitigating measures to dampen the instability growth, thus improving the chance that fusion concepts such as inertial confinement fusion (ICF) are successful. A study of 1D and 2D simulations are presented for investigating RT instability growth in deceleration stage of imploding geometries. Two cases of laser-driven implosion geometry, Cartesian and cylindrical, are used to study late stage deceleration-phase RT instability development on the interior surface of imploding targets. FLASH's hydrodynamic (HD) and magnetohydrodynamic (MHD) modeling capabilities are used for different laser and target parameters in order to study the RT instability and the impact of externally applied magnetic fields on their evolution. Several simulation regimes have been identified that provide novel insight into the impact that a seeded magnetic field can have on RT instability growth and the conditions under which magnetic field stabilization of the RT instability is observable. Finally, future work and recommendations are made.
  • Thumbnail Image
    Design and Analysis of Low Reynolds Number Marine Propellers with Computational Fluid Dynamics (CFD) Transition Modeling
    Webster, John Ackroyd III (Virginia Tech, 2019-08-12)
    Small-scale marine propellers operate at low Reynolds numbers, where laminar-turbulent transition of the boundary layer can impact the distributions of pressure and shear stress on the blade surface. Marine propellers operating at low Reynolds numbers are subject to laminar-turbulent transition of the boundary layer, which impacts the distributions of pressure and shear stress on the blade surface. To design efficient propellers for operation at low Reynolds numbers, transitional effects must be included in the evaluations of propeller performance. In this work, transition modeling techniques in Reynolds Averaged Navier-Stokes computational fluid dynamics (RANS CFD) are utilized to evaluate and design propellers operating at low Reynolds numbers. The Galilean invariant γ transition model with an extension for crossflow transition is coupled to the SSG (Speziale, Sarkar, Gatski) /LRR (Launder, Reece, Rodi) -ω Reynolds stress transport turbulence model, with validation cases performed for flate plate boundary layers, 2-dimensional airfoils, a 3-dimensional wing, and 6:1 prolate spheroids. The performance of the coupled SSG/LRR-ω-γ Reynolds stress transition model for propellers with flow transition is then evaluated using experimental surface streamline and force data from four model-scale marine propellers. A method for the design of low Reynolds number marine propellers is presented using a transition-sensitive lifting line method coupled with the panel method code XFOIL. Initial geometries generated using the lifting-line method are then optimized in RANS CFD using the 2 equation γ-Reθ transition model and an adjoint method to warp the propeller shape to improve the efficiency. Two design studies are performed, including an open water propeller, and a propeller designed for a small autonomous underwater vehicle.
  • Thumbnail Image
    Design, Simulation, and Experimental Validation of a Novel High-Speed Omnidirectional Underwater Propulsion Mechanism
    Njaka, Taylor Dean (Virginia Tech, 2021-01-11)
    This dissertation explores a novel omnidirectional propulsion mechanism for observation-class underwater vehicles, enabling for operation in extreme, hostile, or otherwise high-speed turbulent environments where unprecedented speed and agility are necessary. With a small overall profile, the mechanism consists of two sets of counter-rotating blades operating at frequencies high enough to dampen vibrational effects on onboard sensors. Each rotor is individually powered to allow for roll control via relative motor effort and attached to a swashplate mechanism, providing quick and powerful manipulation of fluid-flow direction in the hull's coordinate frame without the need to track rotor position. The omnidirectional mechanism exploits properties emerging from its continuous counter-rotating blades to generate near-instantaneous forces and moments in six degrees of freedom (DOF) of considerable magnitude, and is designed to allow each DOF to be controlled independently by one of six decoupled control parameters. The work presented in this dissertation validates the mechanism through physical small-scale experimentation, confirming near-instantaneous reaction time, and aligning with computational fluid dynamic (CFD) results presented for the proposed theorized full-scale implementation. Specifically, it is demonstrated that the mechanism can generate sway thrust at 10-20% surge thrust capacity in both simulation and physical tests. It is also shown that the magnitude of forces and moments generated is directly proportional to motor effort and corresponding commands, in par with theory. Any apparent couplings between different control modes are deeply understood and shown to be trivially accounted for, effectively uncoupling all six control parameters. The design, principles, and bullard-pull simulation of the proposed full-scale mechanism and vehicle implementation are then thoroughly discussed. Kinematic and hydrodynamic analyses of the hull and surrounding fluid forces during different maneuvers are presented, followed by the mechanical design and kinematic analysis of each subsystem. To estimate proposed full-scale performance specifications and UUV turbulence rejection, a full six-DOF maneuvering model is constructed from first principles utilizing CFD and regression techniques. This dissertation thoroughly examines the working principles and performance of a novel omnidirectional propulsion mechanism. With the small-scale model and full scale simulation and analysis, the work presented successfully demonstrates the mechanism can generate nearly instantaneous omnidirectional forces underwater in a controlled manner, with application to high-speed agile vehicles in dynamic environments.
  • Thumbnail Image
    The Design, Verification, and Validation of a Personal Hydrofoil Craft
    Dougherty, Hugh Raymond Robert (Virginia Tech, 2024-02-02)
    The VT i-Ship Lab has been assigned the task of designing and building a Personal Hydrofoil Craft capable of carrying two people, featuring the distinctive capabilities of foiling and diving. This thesis examines the attributes of fully submerged hydrofoils and their prospective advancements. Diverse configurations of fully submerged hydrofoils are scrutinized, accompanied by an exploration of their respective stability characteristics. A comprehensive analysis is conducted on the design space trade-offs, incorporating potential flow-based methodologies such as the lifting line and vortex lattice methods, encompassing considerations for the free surface, structural computations, and propulsion optimization. In conjunction with the design study computational fluid dynamics is employed to verify the estimated values and to fine-tune the system allowing for a robust low-fidelity system that can quickly estimate the appropriate hydrofoil arrangement for the desired conditions. Various hydrofoil and craft configurations are explored discussing the trade-offs with a final design being chosen and a thorough mechanical design pursued.
  • Thumbnail Image
    Determining Parameters for a Lagrangian Mechanical System Model of a Submerged Vessel Maneuvering in Waves
    Jung, Se Yong (Virginia Tech, 2020-03-16)
    In this dissertation, an approach for determining parameters for a nonlinear Lagrangian mechanical system model of a submerged vessel maneuvering near waves is presented. The nonlinear model with determined parameters is capable of capturing nonlinear effects neglected by other linear models, and therefore can be applied to improve maneuvering performance and expand the operating envelope for submerged vessels operating in elevated sea states. To begin, a first principles Lagrangian nonlinear maneuvering (LNM) model for a surface-affected submerged vessel derived by using Lagrangian mechanics cite{BattistaPhD2018} is reformulated to allow the application of data from a medium fidelity potential flow code. In the reformulation process, the order of integration and differentiation in the integro-differential parameters are switched and partial derivatives of the Lagrangian function are computed with readily available data from the panel code solution. As a result, all model parameters can be computed individually using the panel code, wherein the need for additional numerical discretization is circumvented in the computation process through use of solutions already performed by the basic panel code, enabling higher accuracy and lower computational cost. Furthermore, incident wave effects are incorporated into the reformulated LNM model to yield a Lagrangian nonlinear maneuvering and seakeeping (LNMS) model. The LNMS model is numerically validated by confirming the proposed methods and by comparing steady and unsteady hydrodynamic force calculations from the LNMS model against panel code computations for various vessel motions in calm water and in plane progressive waves. Finally, methods for computing physically intuitive components of the model parameters, as well as methods for making approximations of the terms accounting for memory effects are presented, leading to a model formulation amenable to control design. By applying the methods proposed in this dissertation, each and every parameter of the Lagrangian mechanical system model of a submerged vessel maneuvering in waves can be obtained accurately and with computational efficiency by using a potential flow panel code. The resulting nonlinear motion model provides higher model fidelity than existing unified maneuvering and seakeeping models, especially in applications such as nonlinear control design and simulation.
  • Thumbnail Image
    Development and Application of Dynamic Architecture Flow Optimization to Assess the Impact of Energy Storage on Naval Ship Mission Effectiveness, System Vulnerability and Recoverability
    Kara, Mustafa Yasin (Virginia Tech, 2022-05-20)
    This dissertation presents the development and application of a naval ship distributed system architecture framework, Architecture Flow Optimization (AFO), Dynamic Architecture Flow Optimization (DAFO), and Energy Storage System (ESS) model in naval ship Concept and Requirements Exploration (CandRE). The particular objective of this dissertation is to determine and assess Energy Storage System (ESS) capacity, charging and discharging capabilities in a complex naval ship system of systems to minimize vulnerability and maximize recoverability and effectiveness. The architecture framework is implemented through integrated Ship Behavior Interaction Models (SBIMs) that include the following: Warfighting Model (WM), Ship Operational Model (OM), Capability Model (CM), and Dynamic Architecture Flow Optimization (DAFO). These models provide a critical interface between logical, physical, and operational architectures, quantifying warfighting and propulsion capabilities through system measures of performance at specific capability nodes. This decomposition greatly simplifies the Mission, Power, and Energy System (MPES) design process for use in CandRE. AFO and DAFO are network-based, linear programming optimization methods used to design and analyze MPESs at a sufficient level of detail to understand system energy flow, define MPES architecture and sizing, model operations, reduce system vulnerability and improve system effectiveness and recoverability with ESS capabilities. AFO incorporates system topologies, energy coefficient component models, preliminary arrangements, and (nominal and damaged) steady state scenarios to minimize the energy flow cost required to satisfy all operational scenario demands and constraints. The refined DAFO applies the same principles as AFO, but adds two more capabilities, Propulsion and ESS charging, and maximizes effectiveness at each scenario timestep. DAFO also integrates with a warfighting model, operational model, and capabilities model that quantify the performance of tasks enabled by capabilities through system measures of performance at specific capability nodes. This dissertation provides a description of the design tools developed to implement these processes and methods, including a ship synthesis model, hullform exploration, MPES explorations and objective attribute metrics for cost, effectiveness and risk, using design of experiments (DOEs) response surface models (RSMs) and Energy Storage System (ESS) applications.
  • Thumbnail Image
    Drag Reduction by Polymeric Additive Solutions
    Clares Pastrana, Jorge Arturo (Virginia Tech, 2023-10-18)
    Historically, the addition of polymers to turbulent flows of Newtonian fluids has been known to effectively reduce turbulent friction drag by up to 80 %. Conducted in the Hydrodynamics Laboratory in Virginia Tech, this research presents a comprehensive analysis into drag reducing effects through experimental, theoretical, and computational analyses. A major focus of this research was the evaluation of one of the newest viscoelastic Reynolds Averaged Navier-Stokes (RANS) turbulence models. Based on the k−ε−v 2−f framework, this model describes the viscoelastic effects of polymer additives using the Finitely Extensible Nonlinear Elastic-Peterlin (FENEP) constitutive model. To evaluate its accuracy, multiple simulation scenarios were benchmarked against Direct Numerical Simulation (DNS) data. Results indicated, that the viscoelastic RANS turbulence model shows a high accuracy against DNS percentages of drag reduced when dealing with higher solvent viscosity to polymer viscosity ratios, but revealed inconsistencies at lower ratios. Additionally, our theoretical and empirical flow rates from the inclined channel were closely aligned. The results of this study highlight the significant capacity of polymer additives to improve energy efficiency in industries that heavily rely on fluids
  • Thumbnail Image
    Dynamic Model of a Small Autonomous Hydrofoil Vessel
    Moon, Heejip (Virginia Tech, 2024-06-06)
    This thesis presents the development of a six degree of freedom nonlinear dynamic model for a single-mast fully submerged hydrofoil vehicle. The aim of the model is to aid in evaluating various model-based controllers for autonomous operation by simulating their performance before implementation in the field. Initially, first principles approach is employed to develop an approximate dynamic model of the vehicle. Prediction of the vehicle motion using the first principles model is then compared with the data from the tow tank experiments to assess the accuracy of the assumptions made in estimating the hydrofoil performance. Additionally, the dynamic model is adjusted to reflect the measured hydrodynamic forces in the tow tank tests. Utilizing the modified dynamic model to simulate the vehicle motion, an initial height controller is designed and tuned in field trials until stable foiling state was achieved. We evaluate the field results and discuss the limitation of employing steady-state tow tank data in establishing the vehicle dynamic model.